1. Field of the Invention
The present invention relates to a graphic display apparatus and a graphic display method capable of displaying a graphic with a high definition using a color display device, and a recording medium for use with such apparatus and method.
2. Description of the Related Art
For example, in a known technique for displaying a graphic, such as a character, a pictorial symbol, etc., on a display apparatus, bit map data which is based on two binary values corresponding to black and white is displayed on a pixel by pixel basis. In this technique, one of a plurality of dots which form a graphic corresponds to one pixel. Pixels corresponding to black dote (portions which form the outline and inside of each graphic) are represented in black, and pixels corresponding to white dots are represented in white.
Further, a technique disclosed in Japanese Laid-Open Publication No. 3-201788 is known as a technique improved from a conventional technique for displaying bit map data on a pixel by pixel basis. According to this improved technique, in a color display apparatus which has sub-pixels corresponding to three color elements, R (red), G (green), and B (blue), the location of a black area can be adjusted at intervals of ⅓ of a pixel, and therefore, oblique lines included in a graphic can be smoothly displayed.
FIG. 39A shows an example of a character “A” of the English alphabet displayed on a display plane 900 of 5 pixels×9 pixels according to the conventional technique for displaying bit map data which is based on two binary values corresponding to black and white on a pixel by pixel basis. In FIG. 39A, each hatched box represents a pixel displayed in black and each open box represents a pixel displayed in white.
FIG. 39B shows bitmap data 904 of the character “A” of the English alphabet displayed on a display plane 900. In FIG. 39B, each bit labeled with “1” corresponds to a black area, and each bit labeled with “0” corresponds to a white area.
In this display technique, a substantial degree of jaggedness occurs along oblique lines of the character “A” as shown in FIG. 39A. Therefore, the oblique lines of the character “A” cannot be viewed by a human eye as smooth oblique lines. In this conventional technique for displaying bit map data which is based on two binary values corresponding to black and white on a pixel by pixel basis, the location of a black area can only be adjusted at intervals of a single pixel. Thus, a character displayed according to this conventional technique cannot be seen by a human eye as a well-defined character because jaggedness occurs along oblique lines or curves of the character. Particularly, when a character is displayed with a small number of dots, a greater degree of jaggedness is observed.
FIG. 40A shows an example of a character “A” of the English alphabet displayed on a display plane 910 of a color display device according to the technique disclosedin Japanese Laid-Open Publication No. 3-201788, which is a technique improved from a conventional technique for displaying bit map data on a pixel by pixel basis.
The display plane 910 has a plurality of pixels 912. Each of the plurality of pixels 912 includes horizontally-arranged sub-pixels 914R, 914G, and 914B. The sub-pixels 914R, 914G, and 914B correspond to the three color elements, R (red), G (green), and B (blue), respectively.
According to this improved conventional technique, binary bit map data which form a character is provided for each of planes, R-plane, G-plane, and B-plane, and when a set of three adjacent sub-pixels are turned off, an area corresponding to the set of three adjacent sub-pixels is displayed in black. Herein, the “plane” means a group of sub-pixels corresponding to any one of the three color elements, R, G, and B. The arrangement order of three sub-pixels may be any of (R. G, B), (G, B, R), and (B, R, G). Thus, the location of a black area represented by a set of three sub-pixels can be adjusted at intervals of a ⅓ pixel, and therefore, oblique lines included in a character can be smoothly displayed. For example, oblique lines included in the character “A” of FIG. 40A result in a smaller degree of jaggedness and are displayed more smoothly as compared with those included in the character “A” of FIG. 39A.
However, this improved conventional technique requires a larger amount of data for displaying a character having a same size, for example, requires a memory three times larger than that required in the conventional technique for displaying bit map data on a pixel by pixel basis. This is because binary bit map data which form a character must be prepared for each of the planes (R-plane, G-plane, and B-plane).
FIG. 40B shows bit map data 916 according to the above improved conventional technique. The bit map data 916 includes bit map data 916R for the R-plane, bit map data 916G for the G-plane, and bit map data 916B for the B-plane. As shown, the bit map data 916 has a data amount three times larger than that of the bit map data 904 (FIG. 39B) of the conventional technique for displaying bit map data on a pixel by pixel basis.
Furthermore, according to the above-described improved conventional technique, the arrangement order of sub-pixels to be turned off is not constant, i.e., may be any of (R, G, B), (G, B. R), and (B, R, G), and color mixture is insufficient at an interface between a region of sub-pixels to be turned on (white area) and a region of sub-pixels to be turned off (black area). As a result, a noticeable color noise occurs at the interface therebetween. Furthermore, a data structure of the bit map data is different from those employed widely in the conventional techniques, and therefore, this data structure cannot be widely applied to various conventional information display apparatuses.